Portable devices comprise a battery as an energy source. A battery may comprise a single cell or multiple cells in series and/or parallel. Voltage available at the terminals of the battery fluctuates during a charge-discharge cycle. The battery of a device powers multiple components of the device with variable current needs. Battery characteristics (for example the battery internal resistance or the equivalent series resistance) and battery operation are affected by environmental and temporal factors, such as temperature and age of the battery, causing the operation of the portable device to be affected.